Hermetically sealed disk files have been known for some time, as shown, in U.S. Pat. No. 4,367,503 granted to Treseder, one of the present co-inventors. The advantages of hermetically sealing a magnetic or optical disk file are several. First, the file can be operated in a low density, inert gas atmosphere such as helium which reduces the aerodynamic drag between the disks and their associated read-write heads by a factor of approximately 5 to 1 compared to operation in air. At the same time, the helium gas more effectively conducts away heat generated during operation of the disk file.
A significant difficulty to be overcome when a disk file is hermetically sealed is to design the housing so that it will readily accommodate variations between its internal pressure and the ambient atmospheric pressure. Such variations can arise from normal temperature changes during operation, from changes in atmospheric pressure and, in an extreme instance, from extraordinary changes in ambient pressure during air shipment. In the latter case, a differential pressure of approximately 4 psi can be experienced.
FIG. 1 of this application shows a schematic, elevation view of a hermetically sealed disk file of the type disclosed in the Treseder patent. The essentially circular base plate 10 is provided at an off-center location with a stepped bore 12. On one side of plate 10 is attached, a frusto-conical bearing support member 14 which supports on its inner diameter a pair of spindle bearings 16,18. Within these bearings, a hollow spindle 20 is rotatably supported; and a spindle hub 22 is attached to the upper end of spindle 20. A plurality of disks 24, separated by spacing rings 26 and held in place on hub 22 by disk clamp 28, are provided for storage and retrieval of data.
A quill shaft 30 extends through hollow spindle 20 to the opposite side of base plate 10 where it is operatively connected to the rotor 32 of a spindle drive motor 34. Rotor 32 is mounted for rotation in a pair of rotor bearings 36,38 supported within the stator assembly 40 of motor 24. Motor 34, as illustrated, is attached to the underside of base plate 10. As indicated schematically, a disk actuator assembly 42 is supported on base plate 10 next to the spindle and disk assembly so that its read-write heads 44 can be moved into position to receive or transmit data from or to the disks 24. A suitable actuator for such an application is disclosed in U.S. Pat. No. 3,849,800, for example.
The previously described structure is enclosed within a deep drawn, corrugated sheet metal enclosure 46 which is closed at its upper end by a corrugated sheet metal cover 48. Enclosure 46 and cover 48 are hermetically joined to one another by a conventional double seamed viscoelastic seal 50 such as is commonly used in the canning industry. Typical materials for the viscoelastic material used in such seals are disclosed in the Treseder patent. A plurality of mounting brackets 52, each having a rounded end 54 are provided to engage an inwardly projecting, circumferentially extending corrugation 56 in enclosure 46. Within the enclosure, base plate 10 is secured to corrugation 56 by means of a clamping ring 58. Finally, power for motor 34 and disk file actuator 42 is brought into the sealed enclosure through an electrical feedthrough connector 60 of a type known in the art.
As can be seen in FIG. 1, a hermetically sealed disk file of the type disclosed in the Treseder patent requires a cylindrical enclosure 46,48 having an outer diameter approximately twice that of the enclosed disks 24. As a result of this, the end panels of the enclosure 46,48 undergo relatively large deflections due to changes in pressure and temperature. The maximum deflection of a circular end panel can be shown to be a function of the diameter of the end panel raised to the fourth power. Thus, a cylindrical enclosure having a diameter approximately twice the diameter of the disk file will deflect approximately 16 times more than would an enclosure having a diameter about equal to that of the disks. In the disk file shown in FIG. 1, the amount of disk deflection can be reduced by increasing the thickness of the end panels; however, this also increases the weight of the disk file.